solves Edit distance in java

Author: anishLearnsToCode

README.txt

@@ -70,6 +70,7 @@
 |  69  | [Sqrt(x)](https://leetcode.com/problems/sqrtx)                                                                                                                         |                                                                    [![Java](assets/java.png)](src/Sqrtx.java) [![Python](assets/python.png)](python/sqrt.py)                                                                     |                                                                                                                                   |
 |  70  | [Climbing Stairs](https://leetcode.com/problems/climbing-stairs)                                                                                                       |                                                          [![Java](assets/java.png)](src/ClimbingStairs.java) [![Python](assets/python.png)](python/climbing_stairs.py)                                                           |                                                                                                                                   |
 |  71  | [Simplify Path](https://leetcode.com/problems/simplify-path)                                                                                                           |                                                                                        [![Java](assets/java.png)](src/SimplifyPath.java)                                                                                         |                                                                                                                                   |
+|  72  | [Edit Distance](https://leetcode.com/problems/edit-distance)                                                                                                           |                                                                                        [![Java](assets/java.png)](src/EditDistance.java)                                                                                         |                                                                                                                                   |
 |  73  | [Set Matrix Zeroes](https://leetcode.com/problems/set-matrix-zeroes)                                                                                                   |                                                                                       [![Java](assets/java.png)](src/SetMatrixZeroes.java)                                                                                       |                                                                                                                                   |
 |  74  | [Search a 2D Matrix](https://leetcode.com/problems/search-a-2d-matrix)                                                                                                 |                                                                                       [![Java](assets/java.png)](src/SearchA2DMatrix.java)                                                                                       |                                                                                                                                   |
 |  75  | [Sort Colors](https://leetcode.com/problems/sort-colors)                                                                                                               |                                                                                         [![Java](assets/java.png)](src/SortColors.java)                                                                                          |                                                                                                                                   |

src/EditDistance.java

@@ -0,0 +1,42 @@
+// https://leetcode.com/problems/edit-distance
+// T: O(m * n)
+// S: O(m * n)
+
+public class EditDistance {
+    public int minDistance(String word1, String word2) {
+        if (word1.isEmpty()) return word2.length();
+        if (word2.isEmpty()) return word1.length();
+
+        final int rows = word1.length() + 1, columns = word2.length() + 1;
+        final int[][] dp = new int[rows][columns];
+
+        dp[0][0] = 0;
+
+        // first row
+        for (int column = 1 ; column < columns ; column++) {
+            dp[0][column] = column;
+        }
+
+        // first column
+        for (int row = 1 ; row < rows ; row++) {
+            dp[row][0] = row;
+        }
+
+        // rest of table
+        for (int row = 1 ; row < rows ; row++) {
+            for (int column = 1 ; column < columns ; column++) {
+                if (word1.charAt(row - 1) == word2.charAt(column - 1)) {
+                    dp[row][column] = dp[row - 1][column - 1];
+                } else {
+                    dp[row][column] = min(dp[row - 1][column - 1], dp[row - 1][column], dp[row][column - 1]) + 1;
+                }
+            }
+        }
+
+        return dp[rows - 1][columns - 1];
+    }
+
+    private int min(int a, int b, int c) {
+        return Math.min(Math.min(a, b), c);
+    }
+}

src/RangeSumQuery2DImmutable.java

@@ -0,0 +1,58 @@
+// https://leetcode.com/problems/range-sum-query-2d-immutable
+// n: matrix.length
+// m: matrix[0].length
+
+
+class NumMatrix {
+
+    final int rows;
+    final int columns;
+    final int[][] dp;
+
+    // T: O(n * m)
+    // S: O(n * m)
+    public NumMatrix(int[][] matrix) {
+        this.rows = matrix.length;
+        this.columns = matrix[0].length;
+        this.dp = new int[rows][columns];
+
+        // first row
+        dp[0][0] = matrix[0][0];
+        for (int column = 1 ; column < columns ; column++) {
+            dp[0][column] = dp[0][column - 1] + matrix[0][column];
+        }
+
+        // first column
+        for (int row = 1 ; row < rows ; row++) {
+            dp[row][0] = dp[row - 1][0] + matrix[row][0];
+        }
+
+        // rest of the matrix
+        for (int row = 1 ; row < rows ; row++) {
+            for (int column = 1 ; column < columns ; column++) {
+                dp[row][column] = dp[row - 1][column] + dp[row][column - 1] - dp[row - 1][column - 1]
+                        + matrix[row][column];
+            }
+        }
+    }
+
+    // T: O(1)
+    // S: O(1)
+    public int sumRegion(int row1, int col1, int row2, int col2) {
+        int result = this.dp[row2][col2];
+        if (row1 > 0) {
+            result -= this.dp[row1 - 1][col2];
+        }
+        if (col1 > 0) {
+            result -= this.dp[row2][col1 - 1];
+        }
+        if (row1 > 0 && col1 > 0) {
+            result += this.dp[row1 - 1][col1 - 1];
+        }
+        return result;
+    }
+}
+
+public class RangeSumQuery2DImmutable {
+
+}